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Research and Development Laboratories 

of the 
Portland Cement Association 



RESEARCH DEPARTMENT 
Bulletin 83 



Studies of 'Salt' Scaling 
of Concrete 

By 
George Verbeck and Paul Klieger 



June, 1957 
Chicago 



Authorized Reprint from 

Highway Research Board Bulletin No. 150 
January, 1956 



Studies of "Salt" Scaling of Concrete 

GEORGE J. VERBECK, Manager, and 
PAUL KLIEGER, Senior Research Engineer, 

Ap|,, >rch Section, H»- ,< ■ ir< ■:■. in 1 Development i 

• rid Cement A 

rd of air-. . rete pav 

lent, However, the n,» vhlch de-icers 

more, (hi-rc Li I i 

ird 
Although h» 

i Km 

.111(1 CHI' 

I 

I 

, .l-i !>♦• ol '•*• 

• I 

A 

in, the m 

>i>. Mm 
in.lllv h» 

• tea 

i 

llll: 

npletely I I 

All |pj| : 

-hown in le a 

a*K rebates * 
<hed in th< uir-dn 

1 



■ 




^tJA% 


y%% 




II *r 




16% ^s^*^ 


u / J^ 




__ — - — -""o* 




NaCI 
Non A /E 




NaCI 
- A /E 




?\< 


■ 




4%^-^ 






_ — ^^82 


. 




16 %> 







100 ,S0 *» b0 ,00 ,50 200 

Number of Cycles of Scaling Test 

Figure 1. Effect of amount of de-icer on surface scaling on non- 
K 1T ~o nt £" lned 8nd air ' entrairied concretes. Scale Test Procedure 
Thmm solution refrozen on slab surface. Aggregates. Elgin, 
Illinois sand and fcau Claire, Wis. crushed gravel (1-in. top size) 
ens: 3 by 6 by 15-in. slabs cured continuously moist for 31 
days prior to test. Cement Content: 6 sacks per cu yd. Slump- 
I 12 to 3 1,2 in. Air Contents: Non A/E - 2-2 percent, A/E - 7.4 

percent. 

to use inundated with a known amount of water. Excess water was drawn off and 
weighed immediately prior to mixing the concrete 

entrame r d a concre!e S01 reSl " * S ° 1Uti ° n WM a<Wed at the ™™ T When P re P a »ng the *,- 

sodium rM^ USed ln th ^ se l scali "g *»* were commercial flake calcium chloride, 
soaium chloride, urea, and ethyl alcohol. 



Fabrication of Specimens 

Each batch contained 1. 30 cu ft of concrete. Batches were mixed for 2% minutes in 
an open-tub mixer of 1%-cu ft capacity. A slump test and an air content determination 
by the pressure method were made on each batch of concrete. 

Generally, two specimens were made for a particular test condition. In a few cases, 
three specimens were made. In all cases, these companion specimens were made on 
different days. 

The specimens used in the scaling test were slabs 3 in. in depth and 6 by 15 in. in 
area. These slabs were cast in watertight steel molds, the molds were filled in two 



5 - 



c 

"5 

u 
to 

CO 
CD 



Calcium Chloride £ 

/ 
/ 
Non%50 Cycles 



Sodium Chloride 



t/Von % 25 Cycles 



*/e 200 Cyc/es 




*/E y SO Qt/c/es 



ro 
u 

CO 



CD 
O 

E 



c 

"(0 

u 
n if) 

Z o 



i 

o 



5 


1 7 1 f T 

, * , Urea 


4 


/ \Non A / E 
\f*\ \ 50 Cyc/es 


3 
Z 

1 


i 


11 \ Y 

v \ \ 

^OOCue/es^^^ 




,<T7 0^^ 





^%-50 Cyc/es 



E_th y I Alcoho l 

A/on a /e 
50 Cyc/es . 




7-, 



Ye -50 Cyc/es 



8 \Z 16 



Solution Concentrations - % by weight 

Figure 2. Effect of amount of de-icer on surface scaling (test pro- 
cedure No. 2 - thaw solution refrozen). 








1 // 




jr 






. 




. r 


,-..c 








' ... 


B . 







/ 



/ / fti*4f [g y '"' 



. 



- 



Ifcl. 



- 



Curing Conditions 

Companion specimens were subjected to two different sets of curing conditions: 

1. Continuously moist cured at 73 deg F for 28 days, followed by an additional 3 
days in the moistroom with the surface of the slab covered with water % in. in depth. 
These will be referred to hereafter as moist cured. 

2. Continuously moist cured at 73 deg F for 14 days, then 14 days in the air of the 
laboratory at 73 deg F and 50 percent relative humidity, followed by an additional 3 



5 ■ 



cn 

c 

U 

l/) 

X3 

CD 



C 
a 



o 



Scale Procedure No. 1 
Non-Air-Entrained ^C^" 
Moist -Cured AX'~\^^'^ 


^-2" 


r~^7s^-^ % 


i&z 




"o% " 


Scale Procedure No. 1 




A /E Moist- Cured 




ic£-> 


slZ 


0% o,a 


nd 5%^ , 



Scale Procedure No.l 
NonVE Air- Dried 



oW ^z-^ar. 



iQ% 



Scale Procedure No.l 
A /e Air- Dried 



t- Z t 4 and S % 




Scale Procedure No. 2 
Nion A /g. Moist -Cured 



0% 



Scale Procedure No. 2 
A /E Moist -Cured 



^^ 




£25 















4% j 


h% 




/l&% 








Sea 


e Procedure No. Z 


Non 


a /e Air- Dried 


I 


/ 







o% 






Scale 


Proced 


jre Na2 






A /£ 


Air- 


Dried 


r 


2%-\ 


.0% 




lfc%^ 




J — ■ — 






L 4 <wd 8 % 



50 100 150 200 50 IOC 150 

Number of Cycles of Scaling Test 

Figure 4. Effect of scale test procedure, concentration of de-icer 
and curing on the surface scaling of non- ai r -entrained and air- 
entrained concretes. Curing: See Table 9 for details. De-icer: 
Commercial flake CaC^. Aggregate: Elgin, Illinois sand and Eau 
Claire, Wis. crushed gravel {1-in. top size). Cement Content: 6 
sacks per cu yd. Slump: 2 to 3 in. Air Contents: Non-A E - 2.2 
percent, A/E - 7.1 percent. 



days in air with the surface of the slab covered with water % in. in depth. These will 
be referred to hereafter as air dried. 

Test Methods 

Three different procedures were followed in determining the surface scaling result- 
ing from the application of different de- 
TABLE 1 icers: 

CHEMICAL COMPOSITION OF . Procedure 1. After freezing 250 ml 

TYPE I BLEND 

PC A Lot No. 18681. Blend of equal parts 
by weight of four Type I cements pur- 
chased locally. 



of water on the surface of a concrete slab 



Major Components 



% 



SiOi 


20.66 




AlaOa 


5.89 




FeaOa 


2.84 




Total CaO 


62.90 




MgO 


2.96 




SO s 


2.16 


CT» 

C 


Ignition Loss 


1.58 


4- 


Minor Components 


% 





Mn 3 3 


0.28 


So! 


Free CaO 


1.09 


00 c 


Insoluble Residue 


0. 18 


q 


Alkalies: 




ro 3 


Na 2 


0.20 


.« 

q5 w 


K 2 


0.54 


E 


Total as Na*0 


0. 56 


3 
Z 






b 8 

i £ 

o 



Hake Calcium Chloride 
Z% Concentration, by wt 
Thaw Solution Refrozen 



^125 Cycles 



50 Cycles 




Air Content of Concrete - % (Pressure) 

re 6. Effect of entrained air on re- 
sistance to surface scaling (scale test 
prodedure -gates: Elgin, 111. 

sand and Lau Claire, His. gravel. Cement 
Content: 6 sacks per cu yd. Slump: 3 in. 
Curing: 14 days moist, 14 days in air plus 
3 days in air *i th water on top surface. 



Tra p Pock 
Sand fr Stone 



o Non A /fc Moist-Cured 
• • m h Air-Dned 
x A/ E Moist-Cured 
A- - Air- Dried 



Elg in Sand ^ 
Eau Claire Gravel 



i 

B B 



o - 


Non */fc 


Moiet-Cxired] 
Air -Dried 


* 


% 


Moist Cured 


A 




Air-C 



J 



12 3 4 

Numerical Scale Rating 
Solution Replaced 

Figure 5. Comparison of scale test pro- 
cedures. 

TABLE 2 

POTENTIAL COMPOUND COMPOSITION 
OF CEMENT 



Compound 



C3S 

C*S 

CsA 

C«AF 

CaSO« 

Free CaO 



% by Wt 


44 


8 


25. 


4 


10. 


8 


8. 


7 


3. 


67 


1. 


09 



in a room maintained at -20 deg F, the 
slab was removed to a room maintained 
at 70 deg F and de-icer was applied im- 
mediately to the ice. Alter thawing, the 
resulting solution was removed, the sur- 
face was rinsed and 250 ml of water was 
placed on the surface for the next freeze 
portion of the cycle. The total time in 
freezer was approximately 18 hours. The 
total time in the thawing room was ap- 
proximately 6 hours. 

Procedure 2. The same conditions 
existed as in No. 1 except that the parti- 
cular solution of de-icer and water was 
kept on the specimen during both the 
freeze and thaw portions of the cycle. 



TABLE 3 

MISCELLANEOUS PHYSICAL TESTS OF CEMENT 

Tests made in accordance with ASTM Standards current in 
December, 1951 (specific gravity determined in water rather 
than kerosene). 



Specific surface, sq cm per 


gram 




Wagner 




1710 


Blame 




3310 


Passing No. 325-mesh, % 




91.1 


Specific gravity, in water 




3.182 


Normal consistency, % 




24.5 


Time of setting: Vic at 






Initial 




3 hr 15 min 


Final 




6 hr 20 min 


Gillmore 






Initial 




4 hr 20 min 


Final 




6 hr 30 min 


Autoclave expansion, % 




0.135 


Air content, 1-4 standard mortar, % 


8.2 



TABLE 4 
DATA ON AGGREGATES 



Source and 
Type 



Fine Aggregate 



Source and % Retained on Sieve Fine- Bulk 24-Hr Mean Linear 

Type No. Indicated ness Sp Gr, Absorption, Thermal Coeff 

1 S 16 30 50 IM Modulus S. S. D. a % by Wt of Expansion, b 

xl0 9 /°F 



Dresser, Wis 
(crushed) 


5 


30 


55 


80 92 2.62 2.918 


1. 14 


4. 74 


Elgin, 111. 
(natural) 


18 


33 


57 


87 95 2.90 2.645 


2.25 


5.73 


Coarse Aggregate 



% Retained on Sieve 
Indicated 



1-in. 



3/ . 

A -in. 



/fe-in. 



No. 4 



Bulk 24-Hr Mean Linear 

Sp Gr, Absorption, Thermal Coeff 
S. S. D. a % by Wt . of Expansion, b 



Dresser, Wis 
(crushed) 





25 


70 


100 


2. 980 


0.20 


4. 74 


Eau Claire, Wis 
(natural) 





25 


70 


100 


2. 693 


1. 33 


5.94 


a Saturated, surface-dry. 
b Dilatometer method. 



TABLE 5 
CONCRETE MDC DATA 



Cement 


Cement NetWC. % Slump Air 
Content, gal. per Sand, in. Content, % 
sacks per sack Abs (pressure) 
cu yd Volume 


Dresser, 


Wis Fine and Coarse Aggregate (Crushed) 


Type I 


6. 7. 2 46 2. 2 2. 1 


Type 1 + 

Vinsol Resin 


5. 8 6.9 42 3.0 7. 1 


Elgin 


111. Fine Aggregate and Eau Claire, Wis 
Coarse Aggregate (Natural) 


Type 1 


6.0 5.2 41 3.2 2.2 


Type I + 
Vinsol Resin 


6. 4. 8 36 3.3 7. 2 



The sodium chloride, calcium chloride, 
and urea solutions were replaced with 
fresh solutions once each week. The 
ethyl alcohol solutions were replaced 
twice each week. 

Procedure 3. In this procedure, the 
specimen was frozen with the surface 
damp (no excess water). On removal to 
the thawing room, the surface was cov- 
ered with 250 ml of solution containing 
the particular amount and type of de-icer 
required. After completion of thawing, 
the solution was removed, and the surface 
was rinsed and drained completely for the 
next freeze portion of the cycle. 



Scale Test 

Specimens: 



TABLE 6 
RESULTS OF SCALING TESTS WITH DIFFERENT DE-ICERS 
Thaw solution refrozen (Procedure 2) 






3- by 6- by 15-in, slabs cured continuously moist for 31 days prior to start of test 
Cement Content: 6 sacks per cu yd, 2\' 2 to 3Vin. slump 

Aggregates: Elgin, Illinois sand and Eau Claire, Wisconsin gravel (1-in. top size) 
Air Contents: Non-A E - 2.2%, A/E - 7. 4% 



Concen- 
tration 
of Soln 
after 
Thawing, 
%by Wt 






Non-A 


Numerical Scale Rating at 
lr-Entrained Concrete 


Ind 


icated Number of Cycles 

Air-Entrained Concrete 


5 15 


2b 


50 


75 


100 


150 200 


5 


15 


25 


50 


7S 


100 


150 


200 














No De-icer 
















0+ 


1- 


1 + 


1 + 


2- 2+ 

















0+ 


0+ 


1- 












Flake Calcium Chlon 


de 














2 

4 

8 

16 


1- 

0+ 




u 
1- 

0+ 



4- 
1+ 

1- 



(70) a 
3- 
2- 
0+ 


3. 

2 

1 


(133) 

3 4 + 
3- (164) 














0+ 





+ 
0+ 








1- 

0+ 
0+ 

1 


1 

1- 

0+ 
(150) 


1+ 

1- 

1- 


Sodium Chlnririp 


2 

4 

8 

16 


2 

u 

0+ 



(25) 
4 + 
0+ 



(35) 
3- 

1 


4- 
2- 


5- 
2 


(108) 
2, 3 + 















o. 






0+ 






1 

0* 

0- 



u 

0+ 
0+ 



3+ 

1 

0+ 




5- 
2 

0+ 



Nrpa 


2 

4 

8 

16 


0+ 
1- 
0+ 



2 
3 

1- 
0+ 


<50> 

3- 
1+ 


5- 
2+ 


(85) 
3- 


(150) 














0+ 





0+ 

+ 






1- 
1- 

0+ 
0+ 


1 
1 

1- 

0+ 


2 

2- 
1 + 
1- 


4- 
4- 
2- 
1- 














Ethyl Alcohol 


















2 

4 

8 

16 


0+ 
(h 
0+ 
G+ 


u 
u 

1 
1 


4 

(50) 
4~ 
3 


(75) 

(60) 
4+ 


(85) 












0+ 





0+ 
0+ 





0+ 
0+ 



0+ 

0+ 
0+ 
0+ 


1 

1+ 
1- 
0* 


2+ 

3- 
2- 
1 + 


3- 
4- 
3- 
2 


a ( ) - Number of cycles at which test was 


discontinued at 


a rating of 5, 











The following listing shows which de-icers and which concretes were used in these 
three procedures: 

Procedure 1 - Calcium Chloride 

Both aggregate combinations 

Non-air-entrained and air-entrained 

Both curing conditions 
Procedure 2 - Calcium Chloride 

Both aggregate combinations 

air-entrained and air-entrained 

Both curing conditions 

Sodium Chloride, Urea, and Ethyl Alcohol 

Elgin sand and Eau Claire gravel 

Non-air-entrained and air-entrained 

Moist-cured concretes only 
Procedure 3 - Calcium Chloride 

Dresser trap rock sand and coarse aggregate 

Non-air-entrained 

Both curing conditions 



At intervals during the sealing test, the surfaces were examined carefully, rated as 
to extent and depth of scale and assigned a numerical rating as follows: - no scaling, 
1 - very slight scaling, 2 - slight to moderate scaling, 3 - moderate scaling, 4 - mod- 
to severe scaling, and 5 - severe scaling. 

TABLE 7 

RB8ULT8 Of 84 AUNG rESTS TRAP ROCK FINE AND COARSE AGGREGATE 

De-icer. Flake calcium chloride 
i M 14 duy.s 3 daya in air with I 

.mp 

1L rgregate (1-in. top 
1% 

Nun* 



i 
2 2 (35) 

i 13-; 

3- (35) 





f 

1-2 4> (163) 

2 o. I ISO) I (53) 

4 

! .50) 

- 
4- (63) 1 ► 4 

Air-Entrained - Moist Cured 

0* 0+ - 

2 0000 0* 0* 1 

'000 

DO 000*1-1 2- 3 (188) 

oooo o a* 

000 O* 000000*1 

000000 

0> 0+ Q» 0* 0* 1- 1> 2- 

Air-Entrained - Air Dried 



2 00000 O* 0^00000000 

000 000000000 

I 

t O* IV O* 00000000 

----- 

000 o oooooooo o b 

i r which te 

-d off abruptly . ;*. . 



10 



TABLE 8 

RESULTS OF SCALING TESTS - ELGIN SAND AND EAU CLAIRE GRAVEL 

Specimens: 3- by 6- by 15-in. slabs De-icer: Flake calcium chloride 

Curing: (a) 31 days moist (b) 14 days moist, 14 days in air plus 3 days in air with water on 

surface 
Cement Content; 6 sacks per cu yd, 2- to 3-in. slump 

Aggregates; Elgin, 111. sand and Eau Claire, vVis. crushed gravel (1-in. top size) 
Air Content: Non-A/E - 2. 2%, A E - 7. 1% 

Concen- ' ' " 

tration 

of Soln Numerical Scale Rating at Indicated Number of Cycles 

Thawing Thaw Solution Replaced (Procedure 1) Thaw Solution Refrozen (Procedure 2) 

% by Wt 5 15 25 50 75 100 150 200 5 15 25 50 75 100 150 200 

Non-Air-Entrained - Moist Cur ed 

1-1+ 2- 2 - . . ~ ~ I 

2 0+2+3 4 5- 0+ 1+ 2- (40) 

3 0+2-3- 4 5 _ . 

4 1-3-3 4+ 5- 0+ 1- 1 + 4 (55) 

6 0+0+3- 4- (138)* ...... 

8 0+0+23-4 5-0+ 1- 1+ 4+ (55) 

10 1- 1-2+3- 4 5- - - - . . . . 

16 1- 1- 2-2+ 3- 3 0+ 1- 2+ (72) 

Non-Air-Entrained - Air Dried 

00000 0+ 0+ ----- - 

000 0+1-2-4+ (55) 

4 0+1-2- (40) 

J 0+ 0+ 0+ 0+ 0. 0+ 0+ 1- 2- 3+ 4- 4+ (125) 

-i? 0+1-1-1-1- 1 1+00003-3+ (150) 

„ Air-Entrained - Moist Cured 

o oooooo 0+ "~ (^ 7Z I 

0+000+0+1-1-2-3 

3 000000 - 

4 o 0+ i+ 2- 
6 000000 0+ - - 

® 0+1-1-1-12- 

io oooooo o o -.:.... 

-i? 0+0+ 0+ 0+ 0+ Q+ Q+ 0+ Q i. i 2- 4- (163) 

. Air-Entrained - Air Dried 

0+0+ 0+ ~ol 7~. 
oooooo 0+0+ 0. 0+ 0+ 0+ 0+ 0+ 

1 oooooo ooooooooo 
x * oooooo o ooooooooo 

-£ 0- °^ CW + 0+ Q, (K O+OOOooo Q Qb 

Number of cycles at which test was discontinued at a rating of 5 
.* Surface shell scaled off, about V^-jn. thick. Discontinued at 237 cycles. 






11 



RESULTS OF SCALING TESTS - TRAP ROCK FINE AND 
COARSE AGGREGATES 

Test Cvcle: Slabs frozen with surface damp (no excess of 
water). Thaw solution placed directly on surface at start 
of thawing period (Procedure 3). 

Specimens: 3- by 6- by 15-in. slabs. De-icer. Flake calcium 
chloride. 

Curing: (a) 31 days moist (b) 14 days moist, 14 days in air 
plus 3 days in air with water on surface. 

Cement Content 6 sacks per cu yd, 2- to 3-in. slump, non- 
air-entrained. 

Aggregates: Dresser, Wisconsin, trap rock fine and coarse 
aggregates (1-in. top size). 

Air Content: 2. 1% 



DISCUSSION OF RESULTS 



Effect of Concentration of Different De- 
Icers on Scale Resistance 



Conceotratioi 














ai Thaw 




Numerical Scale Rating at Indicated 




Solution 






Number of Cycles 






% by Wt 


25 


50 75 


100 


150 25 50 75 


100 


150 























2 


0* 


0+ 0+ 


0+ 


0+000 








4 


U* 


0+ 0+ 


0+ 


0+000 








6 


U 

















12 




















16 











00 









The work of Arnfelt ' has indicated 
that concretes frozen and thawed while im- 
mersed in solutions of different materials 
showed maximum deterioration at rela- 
tively low solution concentrations and that 
further increase in concentration resulted 
in a decrease in deterioration. Field ob- 
servations in this country appeared to in- 
dicate that scaling of concrete pavements 
increased with increase in the amount of 
calcium chloride or rock salt used as de- 
icers. 

Before making a general attack on the 
problem of surface scaling, it was desir- 
able to substantiate Arnfelt' s work using 
four materials as de-icers: calcium chloride, sodium chloride, urea, and ethyl alcohol. 
The concretes used in this portion of the study were made with the Elgin sand and Eau 
Claire gravel. Further information on these concretes is shown in Table 5. 

These concretes were moist cured prior to test. Scale test Procedure 2 was used 
to simulate in some respects Arnfelt' s tests in which the concretes were frozen and 
thawed while immersed in the solution. In Procedure 2, the solution of water and de- 
icer remained on the surface of the specimen during both the freeze and thaw portions 
of the cycle. 

Table 6 and Figure 1 show the effect of concentration of solution on the scale resis- 
tance of these concretes. The non-air-entrained concretes show severe scaling much 
sooner than the air-entrained concretes, with the rate of scaling much greater at solu- 
tion concentrations of 2 and 4 percent than at 0, 8, and 16 percent. These data confirm 
the observations of Arnfelt. Figure 2 shows more clearly the greater amounts of sur- 
face scaling occurring with the intermediate and relatively low concentrations of de- 
icers. 

These data are important with regard to the mechanism by which scaling occurs. 
The opinion advanced most frequently is that the mechanism is primarily a chemical 
attack. If this were true, surface scaling would be expected to increase with an in- 
crease in concentration of de-icer. These tests show that this is not so. In addition, 
the de-icers used in these tests are dissimilar chemically. It appears, therefore, that 
the mechanism producing surface scaling is primarily physical. 



Effect of Test Procedure on Scale 
Resistance 

Tables 7 and 8 show the results of 
scaling tests of non-air-entrained and 
air-entrained concretes made with the 
Dresser trap rock aggregate and the El- 
gin sand and Eau Claire gravel, using 
both Procedure 1 and 2 and calcium chlo- 
ride as the de-icer. In Procedure 1 the 
thaw solution is replaced with fresh water 
for the freeze portion of the cycle; in Pro- 



RESULTS OF SCALING TESTS - ELGIN SAND AND 
EAU CLAIRE GRAVEL 

Scale Test: Thaw solution refrozen (Procedure 2). 
De-icer Flake calcium chloride, 2% ^jlution concentration 

(by weight). 
Specimens: 3- by 6- by 15-in. slabs cured 14 days moist, 14 

days in air plus 3 days in air with water on surface. 
Cement Content: 6 sacks per cu yd, 3-in. slump. 
Aggregates: Elgin, Illinois sand and Eau Claire, Wisconsin 

gravel (1-in. top size). 
Air Content: Agent added at mixer to produce range in air 

contents shown. 



1 "Damage on Concrete Pavements by 
Wintertime Salt Treatment," Arnfelt, 
Harry, Meddelande 66, Statens Vaginstitut, 
Stockholm, 1943. 



Air Content 




Numerical Scs 


le Rating at Indicated 


of Concrete 






Number of 


Cycles 


% 


5 


15 


25 


50 


75 100 125 


2.3 


1- 


1 


2- 


2+ 


3+ 3+ 4- 


3.2 


0+ 


0+ 


0+ 


0+ 


1- 1- 1- 


4. 7 


0+ 


0+ 


0+ 


0+ 


0+0+ 0+ 


6.2 








0+ 


0+ 


0+ 0+ 0+ 


7.5 














0+0+0+ 


9.9 








0+ 


0+ 


0+0+0+ 



12 

cedure 2 the thaw solution is refrozen. Companion concretes were cured continuously 
moist or moist plus a period of air drying prior to test. 

Figures 3 and 4 show the numerical scale ratings as a function of the calcium chlo- 
ride solution concentration for these concretes and test procedures during 200 cycles 
of test. Where scaling has developed, note that, in general, the more severe scaling 
occurs at some intermediate and relatively low solution concentration. The scaling 
which occurs when the thaw solution is refrozen is generally more severe than when 
the solution is replaced. The usual laboratory procedure of replacing the thaw solution 
with fresh water (Procedure 1) apparently does not represent the most severe exposure 
attainable. For the purpose of determining the scale resistance for the most severe 
exposure conditions, the laboratory test should involve refreezing the thaw solution 
(Procedure 2). There appears to be no general relationship between the scaling pro- 
duced by Procedures 1 and 2. Figure 5 shows only that Procedure 2 is generally much 
more severe than Procedure 1. 

Some non-air-entrained concretes, both moist cured and air dried, made with the 
Dresser trap rock aggregate were tested for scale resistance using Procedure 3. The 
results are shown in Table 9. In test Procedure 3 the concrete specimen is frozen with 
the surface damp (no excess water) and the surface is then thawed with the appropriate 
calcium chloride solution. The scale ratings obtained during 150 cycles of test are 
shown in Table 9. No scaling has developed on any of these concretes exposed to cal- 
cium chloride solutions concentrations ranging from to 16 percent, except for some 
very slight scale on the moist cured concretes exposed to the 2 and 4 percent solution 
concentrations. These very same concretes would have scaled rapidly under the test 
conditions of Procedure 1 and 2. It would appear that the scale resistance of the sur- 
face was enhanced by the rapid drying of the top surface of the slab, such as would oc- 
cur when a warm wet specimen is placed in cold atmosphere having a low moisture 
content. 

Effect of Prior Curing on Scale Resistance 

Pavements rarely obtain curing comparable to continuous moist curing in the labora- 
tory. Generally, after a minimum prescribed curing period, the concrete is exposed 
to drying conditions with subsequent rewetting at intervals by rainfall. On rewetting, 
however, the amount of water reabsorbed rarely equals that lost during the drying 
period, unless the period of wetting is exceptionally long. This results in a lowered 
degree of saturation. 

The effect on scale resistance of continuous moist curing and a curing period com- 
prised of both moist curing and air drying is shown in Figures 3 and 4. In almost all 
instances, continuous moist curing resulted in concrete surfaces less resistant to sur- 
face scaling than the concretes which underwent some air drying prior to test. For the 
non-air-entrained concretes, although the period of air drying reduced the amount of 
scaling, the resistance of the surfaces was not satisfactory, with the exception of the 
air-dried concrete made with the Eau Claire aggregate which was tested for scale re- 
sistance by Procedure 1, replacing the thaw solution with fresh water. 

The air-dried air-entrained concretes made with both combinations of aggregates 
showed only very slight scaling during 200 cycles of Procedure 1 or 2. Despite the 
severity of Procedure 2, the period of air drying of the air-entrained concrete's pro- 
duced concretes resistant to 200 cycles of this test procedure. Concrete pavements 
may sometimes be subjected simultaneously to conditions of exposure similar to that of 
Procedure 2 and to low de-icer concentrations. Despite this particularly severe com- 
bination of exposure conditions, air-entrained concrete pavements have an excellent 
performance record, which may in part be the result of periodic air drying of the pave- 
ment surface. Laboratory tests should therefore include tests on air-dried concretes. 

Effect of Amount of Air on Scale Resistance 

From over-all durability considerations, the desired air content for concretes made 
with aggregate of 1-in. maximum size is in the range of 4 to 7 percent based on pi ■ 
vious laboratory tests and field experience. The air-entrained concretes used in this 






13 

study had air contents near the upper limit of this range, since preliminary tests had 
indicated that a combination of continuous moist curing followed by exposure to low de- 
icer concentrations in scale test Procedure 2 (thaw solution refrozen) was an extremely 
severe test. Additional concretes were prepared in order to evaluate the scale resis- 
tance at various air contents within this range. Figure 6 shows some of these data 
which indicate that the concretes with 4. 7 percent air content showed surface scale 
ranging from none to very slight as evidenced by a scale rating of 0+ at 125 cycles. 
For concretes cured and tested in the same manner (see Table 8) and made with the 
same aggregate and an air content of 7. 1 percent, the scale rating at 125 cycles was 
identical. This indicates that an air content at the middle of the recommended range of 
4 to 7 percent for this type of concrete performed as well as the concrete with 7. 1 per- 
cent air content. Further details of these tests are shown in Table 10. 

SUMMARY AND CONCLUSIONS 

These laboratory tests provide new information on the effect of de-icers on the sur- 
face scaling of non-air-entrained and air-entrained concretes, each made with two dif- 
ferent coarse aggregates, cured differently, and tested under a variety of scale test 
procedures. While these tests did not provide data from which a complete concept of 
the mechanism involved can be drawn, they have provided a basis for further study, 
some of which is already under way. 

Based on these laboratory tests, the following statements appear valid: 

1. Chemically dissimilar materials, inorganic or organic, salts or non-salts, which 
function as de-icers also cause "salt" scaling, which more appropriately should be 
called "de-icer scaling. " 

2. Relatively low concentrations (of the order of 2 to 4 percent by weight) of de-icer 
produce more surface scaling than higher concentrations or the absence of de-icer. 

3. On the basis of the foregoing, it appears that the mechanism of surface scaling 
is primarily physical rather than chemical. 

4. Surface scale test procedures greatly influence the rate of scaling. The 
most severe test procedure yet discovered is one in which the concrete is alternately 
frozen and thawed with the de-icer solution remaining on the top surface of the concrete 
rather than being replaced with fresh water prior to each freezing. 

5. No scaling was produced when the concrete surface had no free water on it during 
the freeze portion of the cycle. 

6. A period of air drying of the concretes prior to the start of scaling tests in- 
creased the resistance to surface scaling. Air-entrained concretes treated in this 
manner were immune to the most severe scale test procedure for more than 200 cycles 
of test. 

7. With the fixed cement content and slump as specified by these tests, the concrete 
made with the Elgin sand and Eau Claire gravel showed more resistance to surface 
scaling than the concretes made with the Dresser trap rock fine and coarse aggregate.